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• Table 2. Plant species which constitute minor percentages of total biomass at the experimental pastures at Colstrip, 1Wy ?4,1975. Perennial Grasses _ Needle•and-thread grass Blue grams Thickspike wheatgrass Slender wheatgrass•• Orchard grass!-... Foxtail barley Annul Crasses Japanese brome .. Cheatgrass L_ egumes and Forbs - Cicer milkvetch' r: Sainfoin'. Silverleaf scurfpea„_ .,,,. _ . Wild lettuce Western ragweed _. Waryleaf thistle _ Cudweed sagewort Wild licorice _ . Alfalfa' _ Goldenrod Scarlebglobemallow _ Shrubs and Nalf-shrubs Fourwingsaltbush• - Broom snakeweed Yucca(soapweed) Fanged sagewort False-tarragon sagewort 'Were in the seeded mixture; all others are invaders ••May have been with Western wheatgrass seed. The total forage production wasabout 2,000 Ibs/A, which was far greater than the annual forage production of most native range in the Colstrip area. This resulted in part from large energy inputs through application ofchemical fertilizer. Soil tests N the spring of 1975, however, showed neither more available nitrogen nor phosphorus than on local native range. From this we may assume that the residual nutrients from the application of chemical fertilizers have either been utilized by plants or aze tied up W a form not readily avail- able for plant use. Much of the fertilizer applied may have been leached deep into the soil. A key question that remains to be answered, of course, is whether an acceptable produc- tionlevel can be maintained for sustained forage production. From the clipping data of July, 1975, an estimate of stocking rate was determined. The weight of dry forage per acre was fast obtained frbm the field measurements. This was adjusted to account for the proper utilization of each major plant species. The pounds of dry useable forage per acre thus obtained were divided by the dry weight consump- tion per day of one animal unit. The dry weight consump- tion per day is dependent on the type of animal, age of the animal and weight gain objectives. A conservative figure of 30 pounds per day per animal unit was used. The result of this calculation was stocking rate in animal unit days per acre. This was divided by 30 to give animal unit months per acre,acommon expression for stocking capacity. The values presented in Table 3 should be considered as maximum stock- ingrates.They will need to be adjusted according [o produc• tion~ levels inZOmirtg years. The current stocking capacity of the reseeded spoil is about one and one-half times as much armost local native range. Table 3. Approximate stocking capacity of the experimental grazing pastures at Colstrip on July 24, 1975. Pasture Number Stocking capacity (AUM's/Acre' / 1 1.3 2 1.7 3 1.1 . 4 1.4 5 1.2 6 1.3 Mean l.3 t One AUM/Acre equals one animal unit grazed for one month on one acre, where one animal unit is equivalent to one l,000Ib. row with calf. Grazing habits and cattle health Although quantitative data will be available in the future, there were a number of visual observations concerning live- stock behavior and the degree of forage utilization in the late summer of 1975 grazing period. Smooth bromegrass and tall wheatgrass were the most preferred grass species. Severe defoliation of sweetclover by grasshoppers in mid-summer prevented utilization of this species. Crested wheatgrass, even in advanced stages of dry- ing, was utilized to some extent. Overall, we estimated that about 40 percent of the vegetation was consumed during the First grazing period. Placement of salt on the drier slopes distant from the water tanks of each pasture helped to achieve, on an aerial basis, more uniform grazing than would have occurred with- out i[. No "pullup" of individual plants was observed as we walked the pastures during this grazing period. Some plants were grazed to ground level but crowns were left intact. There appeared to be no adverse affects on cattle health due to a diet of mature reseeded vegetation. Uneasiness was noted the day that cattle were introduced to the pastures, but normal grazing behavior appeared shortly thereafter.